compiler/rustc_codegen_llvm/src/common.rs - rust-lang/rust - Git at Google

 //! Code that is useful in various codegen modules.

 use std::borrow::Borrow;

 use libc::{c_char, c_uint};
 use rustc_abi as abi;
 use rustc_abi::HasDataLayout;
 use rustc_abi::Primitive::Pointer;
 use rustc_ast::Mutability;
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hashes::Hash128;
 use rustc_hir::def_id::DefId;
 use rustc_middle::bug;
 use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::cstore::DllImport;
 use tracing::debug;

 use crate::consts::const_alloc_to_llvm;
 pub(crate) use crate::context::CodegenCx;
 use crate::context::{GenericCx, SCx};
 use crate::llvm::{self, BasicBlock, Bool, ConstantInt, False, Metadata, True};
 use crate::type_::Type;
 use crate::value::Value;

 /*
 * A note on nomenclature of linking: "extern", "foreign", and "upcall".
 *
 * An "extern" is an LLVM symbol we wind up emitting an undefined external
 * reference to. This means "we don't have the thing in this compilation unit,
 * please make sure you link it in at runtime". This could be a reference to
 * C code found in a C library, or rust code found in a rust crate.
 *
 * Most "externs" are implicitly declared (automatically) as a result of a
 * user declaring an extern _module_ dependency; this causes the rust driver
 * to locate an extern crate, scan its compilation metadata, and emit extern
 * declarations for any symbols used by the declaring crate.
 *
 * A "foreign" is an extern that references C (or other non-rust ABI) code.
 * There is no metadata to scan for extern references so in these cases either
 * a header-digester like bindgen, or manual function prototypes, have to
 * serve as declarators. So these are usually given explicitly as prototype
 * declarations, in rust code, with ABI attributes on them noting which ABI to
 * link via.
 *
 * An "upcall" is a foreign call generated by the compiler (not corresponding
 * to any user-written call in the code) into the runtime library, to perform
 * some helper task such as bringing a task to life, allocating memory, etc.
 *
 */

 /// A structure representing an active landing pad for the duration of a basic
 /// block.
 ///
 /// Each `Block` may contain an instance of this, indicating whether the block
 /// is part of a landing pad or not. This is used to make decision about whether
 /// to emit `invoke` instructions (e.g., in a landing pad we don't continue to
 /// use `invoke`) and also about various function call metadata.
 ///
 /// For GNU exceptions (`landingpad` + `resume` instructions) this structure is
 /// just a bunch of `None` instances (not too interesting), but for MSVC
 /// exceptions (`cleanuppad` + `cleanupret` instructions) this contains data.
 /// When inside of a landing pad, each function call in LLVM IR needs to be
 /// annotated with which landing pad it's a part of. This is accomplished via
 /// the `OperandBundleDef` value created for MSVC landing pads.
 pub(crate) struct Funclet<'ll> {
     cleanuppad: &'ll Value,
     operand: llvm::OperandBundleBox<'ll>,
 }

 impl<'ll> Funclet<'ll> {
     pub(crate) fn new(cleanuppad: &'ll Value) -> Self {
         Funclet { cleanuppad, operand: llvm::OperandBundleBox::new("funclet", &[cleanuppad]) }
     }

     pub(crate) fn cleanuppad(&self) -> &'ll Value {
         self.cleanuppad
     }

     pub(crate) fn bundle(&self) -> &llvm::OperandBundle<'ll> {
         self.operand.as_ref()
     }
 }

 impl<'ll, CX: Borrow<SCx<'ll>>> BackendTypes for GenericCx<'ll, CX> {
     type Value = &'ll Value;
     type Metadata = &'ll Metadata;
     // FIXME(eddyb) replace this with a `Function` "subclass" of `Value`.
     type Function = &'ll Value;

     type BasicBlock = &'ll BasicBlock;
     type Type = &'ll Type;
     type Funclet = Funclet<'ll>;

     type DIScope = &'ll llvm::debuginfo::DIScope;
     type DILocation = &'ll llvm::debuginfo::DILocation;
     type DIVariable = &'ll llvm::debuginfo::DIVariable;
 }

 impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
     pub(crate) fn const_array(&self, ty: &'ll Type, elts: &[&'ll Value]) -> &'ll Value {
         let len = u64::try_from(elts.len()).expect("LLVMConstArray2 elements len overflow");
         unsafe { llvm::LLVMConstArray2(ty, elts.as_ptr(), len) }
     }

     pub(crate) fn const_bytes(&self, bytes: &[u8]) -> &'ll Value {
         bytes_in_context(self.llcx(), bytes)
     }

     pub(crate) fn const_get_elt(&self, v: &'ll Value, idx: u64) -> &'ll Value {
         unsafe {
             let idx = c_uint::try_from(idx).expect("LLVMGetAggregateElement index overflow");
             let r = llvm::LLVMGetAggregateElement(v, idx).unwrap();

             debug!("const_get_elt(v={:?}, idx={}, r={:?})", v, idx, r);

             r
         }
     }
 }

 impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
     fn const_null(&self, t: &'ll Type) -> &'ll Value {
         unsafe { llvm::LLVMConstNull(t) }
     }

     fn const_undef(&self, t: &'ll Type) -> &'ll Value {
         unsafe { llvm::LLVMGetUndef(t) }
     }

     fn const_poison(&self, t: &'ll Type) -> &'ll Value {
         unsafe { llvm::LLVMGetPoison(t) }
     }

     fn const_bool(&self, val: bool) -> &'ll Value {
         self.const_uint(self.type_i1(), val as u64)
     }

     fn const_i8(&self, i: i8) -> &'ll Value {
         self.const_int(self.type_i8(), i as i64)
     }

     fn const_i16(&self, i: i16) -> &'ll Value {
         self.const_int(self.type_i16(), i as i64)
     }

     fn const_i32(&self, i: i32) -> &'ll Value {
         self.const_int(self.type_i32(), i as i64)
     }

     fn const_int(&self, t: &'ll Type, i: i64) -> &'ll Value {
         debug_assert!(
             self.type_kind(t) == TypeKind::Integer,
             "only allows integer types in const_int"
         );
         unsafe { llvm::LLVMConstInt(t, i as u64, True) }
     }

     fn const_u8(&self, i: u8) -> &'ll Value {
         self.const_uint(self.type_i8(), i as u64)
     }

     fn const_u32(&self, i: u32) -> &'ll Value {
         self.const_uint(self.type_i32(), i as u64)
     }

     fn const_u64(&self, i: u64) -> &'ll Value {
         self.const_uint(self.type_i64(), i)
     }

     fn const_u128(&self, i: u128) -> &'ll Value {
         self.const_uint_big(self.type_i128(), i)
     }

     fn const_usize(&self, i: u64) -> &'ll Value {
         let bit_size = self.data_layout().pointer_size().bits();
         if bit_size < 64 {
             // make sure it doesn't overflow
             assert!(i < (1 << bit_size));
         }

         self.const_uint(self.isize_ty, i)
     }

     fn const_uint(&self, t: &'ll Type, i: u64) -> &'ll Value {
         debug_assert!(
             self.type_kind(t) == TypeKind::Integer,
             "only allows integer types in const_uint"
         );
         unsafe { llvm::LLVMConstInt(t, i, False) }
     }

     fn const_uint_big(&self, t: &'ll Type, u: u128) -> &'ll Value {
         debug_assert!(
             self.type_kind(t) == TypeKind::Integer,
             "only allows integer types in const_uint_big"
         );
         unsafe {
             let words = [u as u64, (u >> 64) as u64];
             llvm::LLVMConstIntOfArbitraryPrecision(t, 2, words.as_ptr())
         }
     }

     fn const_real(&self, t: &'ll Type, val: f64) -> &'ll Value {
         unsafe { llvm::LLVMConstReal(t, val) }
     }

     fn const_str(&self, s: &str) -> (&'ll Value, &'ll Value) {
         let mut const_str_cache = self.const_str_cache.borrow_mut();
         let str_global = const_str_cache.get(s).copied().unwrap_or_else(|| {
             let sc = self.const_bytes(s.as_bytes());
             let sym = self.generate_local_symbol_name("str");
             let g = self.define_global(&sym, self.val_ty(sc)).unwrap_or_else(|| {
                 bug!("symbol `{}` is already defined", sym);
             });
             llvm::set_initializer(g, sc);
             unsafe {
                 llvm::LLVMSetGlobalConstant(g, True);
                 llvm::LLVMSetUnnamedAddress(g, llvm::UnnamedAddr::Global);
             }
             llvm::set_linkage(g, llvm::Linkage::InternalLinkage);
             // Cast to default address space if globals are in a different addrspace
             let g = self.const_pointercast(g, self.type_ptr());
             const_str_cache.insert(s.to_owned(), g);
             g
         });
         let len = s.len();
         (str_global, self.const_usize(len as u64))
     }

     fn const_struct(&self, elts: &[&'ll Value], packed: bool) -> &'ll Value {
         struct_in_context(self.llcx, elts, packed)
     }

     fn const_vector(&self, elts: &[&'ll Value]) -> &'ll Value {
         let len = c_uint::try_from(elts.len()).expect("LLVMConstVector elements len overflow");
         unsafe { llvm::LLVMConstVector(elts.as_ptr(), len) }
     }

     fn const_to_opt_uint(&self, v: &'ll Value) -> Option<u64> {
         try_as_const_integral(v).and_then(|v| unsafe {
             let mut i = 0u64;
             let success = llvm::LLVMRustConstIntGetZExtValue(v, &mut i);
             success.then_some(i)
         })
     }

     fn const_to_opt_u128(&self, v: &'ll Value, sign_ext: bool) -> Option<u128> {
         try_as_const_integral(v).and_then(|v| unsafe {
             let (mut lo, mut hi) = (0u64, 0u64);
             let success = llvm::LLVMRustConstInt128Get(v, sign_ext, &mut hi, &mut lo);
             success.then_some(hi_lo_to_u128(lo, hi))
         })
     }

     fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, llty: &'ll Type) -> &'ll Value {
         let bitsize = if layout.is_bool() { 1 } else { layout.size(self).bits() };
         match cv {
             Scalar::Int(int) => {
                 let data = int.to_bits(layout.size(self));
                 let llval = self.const_uint_big(self.type_ix(bitsize), data);
                 if matches!(layout.primitive(), Pointer(_)) {
                     unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
                 } else {
                     self.const_bitcast(llval, llty)
                 }
             }
             Scalar::Ptr(ptr, _size) => {
                 let (prov, offset) = ptr.prov_and_relative_offset();
                 let global_alloc = self.tcx.global_alloc(prov.alloc_id());
                 let base_addr = match global_alloc {
                     GlobalAlloc::Memory(alloc) => {
                         // For ZSTs directly codegen an aligned pointer.
                         // This avoids generating a zero-sized constant value and actually needing a
                         // real address at runtime.
                         if alloc.inner().len() == 0 {
                             assert_eq!(offset.bytes(), 0);
                             let llval = self.const_usize(alloc.inner().align.bytes());
                             return if matches!(layout.primitive(), Pointer(_)) {
                                 unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
                             } else {
                                 self.const_bitcast(llval, llty)
                             };
                         } else {
                             let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
                             let alloc = alloc.inner();
                             let value = match alloc.mutability {
                                 Mutability::Mut => self.static_addr_of_mut(init, alloc.align, None),
                                 _ => self.static_addr_of_impl(init, alloc.align, None),
                             };
                             if !self.sess().fewer_names() && llvm::get_value_name(value).is_empty()
                             {
                                 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
                                     let mut hasher = StableHasher::new();
                                     alloc.hash_stable(&mut hcx, &mut hasher);
                                     hasher.finish::<Hash128>()
                                 });
                                 llvm::set_value_name(
                                     value,
                                     format!("alloc_{hash:032x}").as_bytes(),
                                 );
                             }
                             value
                         }
                     }
                     GlobalAlloc::Function { instance, .. } => self.get_fn_addr(instance),
                     GlobalAlloc::VTable(ty, dyn_ty) => {
                         let alloc = self
                             .tcx
                             .global_alloc(self.tcx.vtable_allocation((
                                 ty,
                                 dyn_ty.principal().map(|principal| {
                                     self.tcx.instantiate_bound_regions_with_erased(principal)
                                 }),
                             )))
                             .unwrap_memory();
                         let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
                         let value = self.static_addr_of_impl(init, alloc.inner().align, None);
                         value
                     }
                     GlobalAlloc::Static(def_id) => {
                         assert!(self.tcx.is_static(def_id));
                         assert!(!self.tcx.is_thread_local_static(def_id));
                         self.get_static(def_id)
                     }
                 };
                 let base_addr_space = global_alloc.address_space(self);
                 let llval = unsafe {
                     llvm::LLVMConstInBoundsGEP2(
                         self.type_i8(),
                         // Cast to the required address space if necessary
                         self.const_pointercast(base_addr, self.type_ptr_ext(base_addr_space)),
                         &self.const_usize(offset.bytes()),
                         1,
                     )
                 };
                 if !matches!(layout.primitive(), Pointer(_)) {
                     unsafe { llvm::LLVMConstPtrToInt(llval, llty) }
                 } else {
                     self.const_bitcast(llval, llty)
                 }
             }
         }
     }

     fn const_data_from_alloc(&self, alloc: ConstAllocation<'_>) -> Self::Value {
         const_alloc_to_llvm(self, alloc, /*static*/ false)
     }

     fn const_ptr_byte_offset(&self, base_addr: Self::Value, offset: abi::Size) -> Self::Value {
         unsafe {
             llvm::LLVMConstInBoundsGEP2(
                 self.type_i8(),
                 base_addr,
                 &self.const_usize(offset.bytes()),
                 1,
             )
         }
     }
 }

 /// Get the [LLVM type][Type] of a [`Value`].
 pub(crate) fn val_ty(v: &Value) -> &Type {
     unsafe { llvm::LLVMTypeOf(v) }
 }

 pub(crate) fn bytes_in_context<'ll>(llcx: &'ll llvm::Context, bytes: &[u8]) -> &'ll Value {
     unsafe {
         let ptr = bytes.as_ptr() as *const c_char;
         llvm::LLVMConstStringInContext2(llcx, ptr, bytes.len(), True)
     }
 }

 fn struct_in_context<'ll>(
     llcx: &'ll llvm::Context,
     elts: &[&'ll Value],
     packed: bool,
 ) -> &'ll Value {
     let len = c_uint::try_from(elts.len()).expect("LLVMConstStructInContext elements len overflow");
     unsafe { llvm::LLVMConstStructInContext(llcx, elts.as_ptr(), len, packed as Bool) }
 }

 #[inline]
 fn hi_lo_to_u128(lo: u64, hi: u64) -> u128 {
     ((hi as u128) << 64) | (lo as u128)
 }

 fn try_as_const_integral(v: &Value) -> Option<&ConstantInt> {
     unsafe { llvm::LLVMIsAConstantInt(v) }
 }

 pub(crate) fn get_dllimport<'tcx>(
     tcx: TyCtxt<'tcx>,
     id: DefId,
     name: &str,
 ) -> Option<&'tcx DllImport> {
     tcx.native_library(id)
         .and_then(|lib| lib.dll_imports.iter().find(|di| di.name.as_str() == name))
 }

 /// Extension trait for explicit casts to `*const c_char`.
 pub(crate) trait AsCCharPtr {
     /// Equivalent to `self.as_ptr().cast()`, but only casts to `*const c_char`.
     fn as_c_char_ptr(&self) -> *const c_char;
 }

 impl AsCCharPtr for str {
     fn as_c_char_ptr(&self) -> *const c_char {
         self.as_ptr().cast()
     }
 }

 impl AsCCharPtr for [u8] {
     fn as_c_char_ptr(&self) -> *const c_char {
         self.as_ptr().cast()
     }
 }
	//! Code that is useful in various codegen modules.

	use std::borrow::Borrow;

	use libc::{c_char, c_uint};
	use rustc_abi as abi;
	use rustc_abi::HasDataLayout;
	use rustc_abi::Primitive::Pointer;
	use rustc_ast::Mutability;
	use rustc_codegen_ssa::common::TypeKind;
	use rustc_codegen_ssa::traits::*;
	use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
	use rustc_hashes::Hash128;
	use rustc_hir::def_id::DefId;
	use rustc_middle::bug;
	use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
	use rustc_middle::ty::TyCtxt;
	use rustc_session::cstore::DllImport;
	use tracing::debug;

	use crate::consts::const_alloc_to_llvm;
	pub(crate) use crate::context::CodegenCx;
	use crate::context::{GenericCx, SCx};
	use crate::llvm::{self, BasicBlock, Bool, ConstantInt, False, Metadata, True};
	use crate::type_::Type;
	use crate::value::Value;

	/*
	* A note on nomenclature of linking: "extern", "foreign", and "upcall".
	*
	* An "extern" is an LLVM symbol we wind up emitting an undefined external
	* reference to. This means "we don't have the thing in this compilation unit,
	* please make sure you link it in at runtime". This could be a reference to
	* C code found in a C library, or rust code found in a rust crate.
	*
	* Most "externs" are implicitly declared (automatically) as a result of a
	* user declaring an extern _module_ dependency; this causes the rust driver
	* to locate an extern crate, scan its compilation metadata, and emit extern
	* declarations for any symbols used by the declaring crate.
	*
	* A "foreign" is an extern that references C (or other non-rust ABI) code.
	* There is no metadata to scan for extern references so in these cases either
	* a header-digester like bindgen, or manual function prototypes, have to
	* serve as declarators. So these are usually given explicitly as prototype
	* declarations, in rust code, with ABI attributes on them noting which ABI to
	* link via.
	*
	* An "upcall" is a foreign call generated by the compiler (not corresponding
	* to any user-written call in the code) into the runtime library, to perform
	* some helper task such as bringing a task to life, allocating memory, etc.
	*
	*/

	/// A structure representing an active landing pad for the duration of a basic
	/// block.
	///
	/// Each `Block` may contain an instance of this, indicating whether the block
	/// is part of a landing pad or not. This is used to make decision about whether
	/// to emit `invoke` instructions (e.g., in a landing pad we don't continue to
	/// use `invoke`) and also about various function call metadata.
	///
	/// For GNU exceptions (`landingpad` + `resume` instructions) this structure is
	/// just a bunch of `None` instances (not too interesting), but for MSVC
	/// exceptions (`cleanuppad` + `cleanupret` instructions) this contains data.
	/// When inside of a landing pad, each function call in LLVM IR needs to be
	/// annotated with which landing pad it's a part of. This is accomplished via
	/// the `OperandBundleDef` value created for MSVC landing pads.
	pub(crate) struct Funclet<'ll> {
	cleanuppad: &'ll Value,
	operand: llvm::OperandBundleBox<'ll>,
	}

	impl<'ll> Funclet<'ll> {
	pub(crate) fn new(cleanuppad: &'ll Value) -> Self {
	Funclet { cleanuppad, operand: llvm::OperandBundleBox::new("funclet", &[cleanuppad]) }
	}

	pub(crate) fn cleanuppad(&self) -> &'ll Value {
	self.cleanuppad
	}

	pub(crate) fn bundle(&self) -> &llvm::OperandBundle<'ll> {
	self.operand.as_ref()
	}
	}

	impl<'ll, CX: Borrow<SCx<'ll>>> BackendTypes for GenericCx<'ll, CX> {
	type Value = &'ll Value;
	type Metadata = &'ll Metadata;
	// FIXME(eddyb) replace this with a `Function` "subclass" of `Value`.
	type Function = &'ll Value;

	type BasicBlock = &'ll BasicBlock;
	type Type = &'ll Type;
	type Funclet = Funclet<'ll>;

	type DIScope = &'ll llvm::debuginfo::DIScope;
	type DILocation = &'ll llvm::debuginfo::DILocation;
	type DIVariable = &'ll llvm::debuginfo::DIVariable;
	}

	impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
	pub(crate) fn const_array(&self, ty: &'ll Type, elts: &[&'ll Value]) -> &'ll Value {
	let len = u64::try_from(elts.len()).expect("LLVMConstArray2 elements len overflow");
	unsafe { llvm::LLVMConstArray2(ty, elts.as_ptr(), len) }
	}

	pub(crate) fn const_bytes(&self, bytes: &[u8]) -> &'ll Value {
	bytes_in_context(self.llcx(), bytes)
	}

	pub(crate) fn const_get_elt(&self, v: &'ll Value, idx: u64) -> &'ll Value {
	unsafe {
	let idx = c_uint::try_from(idx).expect("LLVMGetAggregateElement index overflow");
	let r = llvm::LLVMGetAggregateElement(v, idx).unwrap();

	debug!("const_get_elt(v={:?}, idx={}, r={:?})", v, idx, r);

	r
	}
	}
	}

	impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
	fn const_null(&self, t: &'ll Type) -> &'ll Value {
	unsafe { llvm::LLVMConstNull(t) }
	}

	fn const_undef(&self, t: &'ll Type) -> &'ll Value {
	unsafe { llvm::LLVMGetUndef(t) }
	}

	fn const_poison(&self, t: &'ll Type) -> &'ll Value {
	unsafe { llvm::LLVMGetPoison(t) }
	}

	fn const_bool(&self, val: bool) -> &'ll Value {
	self.const_uint(self.type_i1(), val as u64)
	}

	fn const_i8(&self, i: i8) -> &'ll Value {
	self.const_int(self.type_i8(), i as i64)
	}

	fn const_i16(&self, i: i16) -> &'ll Value {
	self.const_int(self.type_i16(), i as i64)
	}

	fn const_i32(&self, i: i32) -> &'ll Value {
	self.const_int(self.type_i32(), i as i64)
	}

	fn const_int(&self, t: &'ll Type, i: i64) -> &'ll Value {
	debug_assert!(
	self.type_kind(t) == TypeKind::Integer,
	"only allows integer types in const_int"
	);
	unsafe { llvm::LLVMConstInt(t, i as u64, True) }
	}

	fn const_u8(&self, i: u8) -> &'ll Value {
	self.const_uint(self.type_i8(), i as u64)
	}

	fn const_u32(&self, i: u32) -> &'ll Value {
	self.const_uint(self.type_i32(), i as u64)
	}

	fn const_u64(&self, i: u64) -> &'ll Value {
	self.const_uint(self.type_i64(), i)
	}

	fn const_u128(&self, i: u128) -> &'ll Value {
	self.const_uint_big(self.type_i128(), i)
	}

	fn const_usize(&self, i: u64) -> &'ll Value {
	let bit_size = self.data_layout().pointer_size().bits();
	if bit_size < 64 {
	// make sure it doesn't overflow
	assert!(i < (1 << bit_size));
	}

	self.const_uint(self.isize_ty, i)
	}

	fn const_uint(&self, t: &'ll Type, i: u64) -> &'ll Value {
	debug_assert!(
	self.type_kind(t) == TypeKind::Integer,
	"only allows integer types in const_uint"
	);
	unsafe { llvm::LLVMConstInt(t, i, False) }
	}

	fn const_uint_big(&self, t: &'ll Type, u: u128) -> &'ll Value {
	debug_assert!(
	self.type_kind(t) == TypeKind::Integer,
	"only allows integer types in const_uint_big"
	);
	unsafe {
	let words = [u as u64, (u >> 64) as u64];
	llvm::LLVMConstIntOfArbitraryPrecision(t, 2, words.as_ptr())
	}
	}

	fn const_real(&self, t: &'ll Type, val: f64) -> &'ll Value {
	unsafe { llvm::LLVMConstReal(t, val) }
	}

	fn const_str(&self, s: &str) -> (&'ll Value, &'ll Value) {
	let mut const_str_cache = self.const_str_cache.borrow_mut();
	let str_global = const_str_cache.get(s).copied().unwrap_or_else(\|\| {
	let sc = self.const_bytes(s.as_bytes());
	let sym = self.generate_local_symbol_name("str");
	let g = self.define_global(&sym, self.val_ty(sc)).unwrap_or_else(\|\| {
	bug!("symbol `{}` is already defined", sym);
	});
	llvm::set_initializer(g, sc);
	unsafe {
	llvm::LLVMSetGlobalConstant(g, True);
	llvm::LLVMSetUnnamedAddress(g, llvm::UnnamedAddr::Global);
	}
	llvm::set_linkage(g, llvm::Linkage::InternalLinkage);
	// Cast to default address space if globals are in a different addrspace
	let g = self.const_pointercast(g, self.type_ptr());
	const_str_cache.insert(s.to_owned(), g);
	g
	});
	let len = s.len();
	(str_global, self.const_usize(len as u64))
	}

	fn const_struct(&self, elts: &[&'ll Value], packed: bool) -> &'ll Value {
	struct_in_context(self.llcx, elts, packed)
	}

	fn const_vector(&self, elts: &[&'ll Value]) -> &'ll Value {
	let len = c_uint::try_from(elts.len()).expect("LLVMConstVector elements len overflow");
	unsafe { llvm::LLVMConstVector(elts.as_ptr(), len) }
	}

	fn const_to_opt_uint(&self, v: &'ll Value) -> Option<u64> {
	try_as_const_integral(v).and_then(\|v\| unsafe {
	let mut i = 0u64;
	let success = llvm::LLVMRustConstIntGetZExtValue(v, &mut i);
	success.then_some(i)
	})
	}

	fn const_to_opt_u128(&self, v: &'ll Value, sign_ext: bool) -> Option<u128> {
	try_as_const_integral(v).and_then(\|v\| unsafe {
	let (mut lo, mut hi) = (0u64, 0u64);
	let success = llvm::LLVMRustConstInt128Get(v, sign_ext, &mut hi, &mut lo);
	success.then_some(hi_lo_to_u128(lo, hi))
	})
	}

	fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, llty: &'ll Type) -> &'ll Value {
	let bitsize = if layout.is_bool() { 1 } else { layout.size(self).bits() };
	match cv {
	Scalar::Int(int) => {
	let data = int.to_bits(layout.size(self));
	let llval = self.const_uint_big(self.type_ix(bitsize), data);
	if matches!(layout.primitive(), Pointer(_)) {
	unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
	} else {
	self.const_bitcast(llval, llty)
	}
	}
	Scalar::Ptr(ptr, _size) => {
	let (prov, offset) = ptr.prov_and_relative_offset();
	let global_alloc = self.tcx.global_alloc(prov.alloc_id());
	let base_addr = match global_alloc {
	GlobalAlloc::Memory(alloc) => {
	// For ZSTs directly codegen an aligned pointer.
	// This avoids generating a zero-sized constant value and actually needing a
	// real address at runtime.
	if alloc.inner().len() == 0 {
	assert_eq!(offset.bytes(), 0);
	let llval = self.const_usize(alloc.inner().align.bytes());
	return if matches!(layout.primitive(), Pointer(_)) {
	unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
	} else {
	self.const_bitcast(llval, llty)
	};
	} else {
	let init = const_alloc_to_llvm(self, alloc, /static/ false);
	let alloc = alloc.inner();
	let value = match alloc.mutability {
	Mutability::Mut => self.static_addr_of_mut(init, alloc.align, None),
	_ => self.static_addr_of_impl(init, alloc.align, None),
	};
	if !self.sess().fewer_names() && llvm::get_value_name(value).is_empty()
	{
	let hash = self.tcx.with_stable_hashing_context(\|mut hcx\| {
	let mut hasher = StableHasher::new();
	alloc.hash_stable(&mut hcx, &mut hasher);
	hasher.finish::<Hash128>()
	});
	llvm::set_value_name(
	value,
	format!("alloc_{hash:032x}").as_bytes(),
	);
	}
	value
	}
	}
	GlobalAlloc::Function { instance, .. } => self.get_fn_addr(instance),
	GlobalAlloc::VTable(ty, dyn_ty) => {
	let alloc = self
	.tcx
	.global_alloc(self.tcx.vtable_allocation((
	ty,
	dyn_ty.principal().map(\|principal\| {
	self.tcx.instantiate_bound_regions_with_erased(principal)
	}),
	)))
	.unwrap_memory();
	let init = const_alloc_to_llvm(self, alloc, /static/ false);
	let value = self.static_addr_of_impl(init, alloc.inner().align, None);
	value
	}
	GlobalAlloc::Static(def_id) => {
	assert!(self.tcx.is_static(def_id));
	assert!(!self.tcx.is_thread_local_static(def_id));
	self.get_static(def_id)
	}
	};
	let base_addr_space = global_alloc.address_space(self);
	let llval = unsafe {
	llvm::LLVMConstInBoundsGEP2(
	self.type_i8(),
	// Cast to the required address space if necessary
	self.const_pointercast(base_addr, self.type_ptr_ext(base_addr_space)),
	&self.const_usize(offset.bytes()),
	1,
	)
	};
	if !matches!(layout.primitive(), Pointer(_)) {
	unsafe { llvm::LLVMConstPtrToInt(llval, llty) }
	} else {
	self.const_bitcast(llval, llty)
	}
	}
	}
	}

	fn const_data_from_alloc(&self, alloc: ConstAllocation<'_>) -> Self::Value {
	const_alloc_to_llvm(self, alloc, /static/ false)
	}

	fn const_ptr_byte_offset(&self, base_addr: Self::Value, offset: abi::Size) -> Self::Value {
	unsafe {
	llvm::LLVMConstInBoundsGEP2(
	self.type_i8(),
	base_addr,
	&self.const_usize(offset.bytes()),
	1,
	)
	}
	}
	}

	/// Get the [LLVM type][Type] of a [`Value`].
	pub(crate) fn val_ty(v: &Value) -> &Type {
	unsafe { llvm::LLVMTypeOf(v) }
	}

	pub(crate) fn bytes_in_context<'ll>(llcx: &'ll llvm::Context, bytes: &[u8]) -> &'ll Value {
	unsafe {
	let ptr = bytes.as_ptr() as *const c_char;
	llvm::LLVMConstStringInContext2(llcx, ptr, bytes.len(), True)
	}
	}

	fn struct_in_context<'ll>(
	llcx: &'ll llvm::Context,
	elts: &[&'ll Value],
	packed: bool,
	) -> &'ll Value {
	let len = c_uint::try_from(elts.len()).expect("LLVMConstStructInContext elements len overflow");
	unsafe { llvm::LLVMConstStructInContext(llcx, elts.as_ptr(), len, packed as Bool) }
	}

	#[inline]
	fn hi_lo_to_u128(lo: u64, hi: u64) -> u128 {
	((hi as u128) << 64) \| (lo as u128)
	}

	fn try_as_const_integral(v: &Value) -> Option<&ConstantInt> {
	unsafe { llvm::LLVMIsAConstantInt(v) }
	}

	pub(crate) fn get_dllimport<'tcx>(
	tcx: TyCtxt<'tcx>,
	id: DefId,
	name: &str,
	) -> Option<&'tcx DllImport> {
	tcx.native_library(id)
	.and_then(\|lib\| lib.dll_imports.iter().find(\|di\| di.name.as_str() == name))
	}

	/// Extension trait for explicit casts to `*const c_char`.
	pub(crate) trait AsCCharPtr {
	/// Equivalent to `self.as_ptr().cast()`, but only casts to `*const c_char`.
	fn as_c_char_ptr(&self) -> *const c_char;
	}

	impl AsCCharPtr for str {
	fn as_c_char_ptr(&self) -> *const c_char {
	self.as_ptr().cast()
	}
	}

	impl AsCCharPtr for [u8] {
	fn as_c_char_ptr(&self) -> *const c_char {
	self.as_ptr().cast()
	}
	}